[CVE-2026-53276][MODERATE 7.0] Bluetooth: ISO: Fix a use-after-free of the hci_conn pointer

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-53276
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: Bluetooth: ISO: Fix a use-after-free of the hci_conn pointer
Commit: d324b8aa20bd3c3394e3647dc22491d88f3f4e7a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d324b8aa20bd3c3394e3647dc22491d88f3f4e7a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53276
Analysis date: Mon, 29 Jun 2026 12:49:16 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
Bluetooth ISO rebind can dereference a freed `hci_conn` pointer after dropping the socket lock, allowing a local user with Bluetooth ISO socket access to race close against rebind and potentially crash the kernel.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-53276 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53276

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53276	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'Bluetooth ISO rebind can dereference a stale hci_conn pointer because iso_sock_rebind_bc caches the connection object and then drops the socket lock before taking the HCI device lock. A concurrent close can free the connection during this unlocked window, after which hci_dev_lock may operate on data reached through freed memory. For the CVSS the PR:L is selected because triggering requires local code execution through Bluetooth ISO socket operations and concurrent close or rebind activity, but does not normally require full administrative control. The issue is not directly network reachable and is triggered through a local Bluetooth socket control path. Impact is at least a local denial of service via kernel crash. In the paranoid score it may allow confidentiality and integrity impact because the stale hci_conn memory can be dereferenced after free and the pointer may influence later locking or object access.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-53276  SKIP The Fixes patch not applied yet, so unlikely that actual: d3413703d5f8b7d1e6f514f9440ed5da1bc30796 YES  NO NO unknown 	MAYBE	REMOTE UAF NETWORK KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  Triggering appears to require local code using Bluetooth ISO socket operations, not full administrative control.

* Memory corruption, weak primitive: +1
  This is a race-based UAF/stale pointer dereference of `hci_conn`. The patch does not show attacker-controlled reclaim, write-after-free, callback dispatch, type confusion, or arbitrary write.

* Real lifetime corruption: +1
  The cached `bis` pointer can outlive the connection after `release_sock()` allows concurrent `close()` to free it.

* Reliable kernel crash / strong DoS: +1
  Dereferencing `bis->hdev` after free can plausibly crash the kernel.

* Broad/common subsystem exposure: +1 in paranoid scoring
  Bluetooth is a broadly shipped kernel subsystem, though ISO-specific reachability depends on kernel config and hardware/runtime support.

Subtract / limiting factors:

* Hard or unreliable race: -1 in conservative scoring
  The bug requires hitting an unlocked window between `release_sock()` and `hci_dev_lock()`.

* Race-UAF downgrade rule applied
  No Weak LPE bonus. No confidentiality bonus. No integrity bonus. Conservative score capped at 4 and paranoid score capped at 5.

## 3. Reachability analysis

A local process with access to Bluetooth ISO socket operations can plausibly trigger the bug by racing rebind activity against socket close. This does not appear directly network reachable. A remote Bluetooth peer may influence connection state in some scenarios, but the patch describes the vulnerable action as a local socket control path, so remote reachability is not counted.

Namespaces and containers may matter if Bluetooth socket access is delegated into a container or to a reduced-privilege service. In normal host deployments, this is local PR:L rather than PR:H. The path also depends on Bluetooth ISO support and relevant runtime availability, so it is not as universally reachable as core TCP/IP.

## 4. Severity interpretation

This behaves more like an Actionable Moderate than an ordinary Moderate because it is a real kernel lifetime bug in a socket path. The realistic demonstrated impact is local DoS through UAF dereference and kernel crash.

Theoretical privilege escalation is not strongly supported by the patch because there is no demonstrated reclaim, overwrite, callback, type confusion, or refcount takeover primitive. Paranoid handling still reaches 5 because kernel UAF races historically deserve manual review, especially in externally exposed local socket subsystems.

## 5. One-sentence report phrase

Bluetooth ISO rebind can dereference a freed `hci_conn` pointer after dropping the socket lock, allowing a local user with Bluetooth ISO socket access to race close against rebind and potentially crash the kernel.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

This is a race-based kernel UAF in Bluetooth socket code. The current evidence supports DoS more than LPE, but lifetime corruption in a local socket interface should not be auto-closed without review.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: Bluetooth: ISO: Fix a use-after-free of the hci_conn pointer
Commit: d324b8aa20bd3c3394e3647dc22491d88f3f4e7a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d324b8aa20bd3c3394e3647dc22491d88f3f4e7a

Commit description:

In iso_sock_rebind_bc(), the bis pointer is cached, then the socket lock is
dropped:
	bis = iso_pi(sk)->conn->hcon;
	/* Release the socket before lookups since that requires hci_dev_lock
	 * which shall not be acquired while holding sock_lock for proper
	 * ordering.
	 */
	release_sock(sk);
	hci_dev_lock(bis->hdev);

During the unlocked window, could a concurrent close() destroy the connection
and free the bis structure, causing hci_dev_lock(bis->hdev) to access memory
after it is freed, fix this by using the hdev reference which was safely
acquired via iso_conn_get_hdev().

Fixes: d341370 ("Bluetooth: ISO: Add support to bind to trigger PAST")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/bluetooth/iso.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d324b8aa20bd3c3394e3647dc22491d88f3f4e7a

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-53276 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53276

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 4
  Paranoid ActionableScore: 5

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).